Many electronic devices, which connect to external circuits through connectors, are required to be waterproofed. For example, an automotive electronic control unit is required to be airtight, since the electronic control unit is generally mounted in a location having moisture, or where the temperature greatly varies. For an electronic device required to be airtight, there is a known structure in which a seal is disposed between an enclosure that contains an electronic circuit and a connector.
A conventions electronic device 800 is shown in FIG. 12, which includes a enclosure 803, a connector 802 fixed to the enclosure 803 with an adhesive resin 804, and a circuit board 801 fixed to the connector 802. Incidentally, illustration of components mounted on the circuit board 801, except the connector 802 is omitted. Also, illustration of an adhesive resin, which fills a space between the bottom surface of the enclosure 803 and the undersurface of the circuit board 801 so as to improve its resistance to vibration and heat radiation property, is omitted. The known electronic device 800 is assembled in such a manner that the connector 802 is fixed to and integrated with the circuit board 801 first, and subsequently, the circuit board 801 is installed in and secured to the enclosure 803. When the circuit board 801 is installed in the enclosure 803, the edge of a through-hole portion of the enclosure 803 is located at a groove formed on the circumference of the connector 802. The groove of the connector 802 is filled with an adhesive resin 804, thereby sealing a gap between the connector 802 and the enclosure 803. In this assembly, the enclosure 803, the connector 802 and the circuit board 801 are integrated.
The electronic device 800 shown in FIG. 12 has a known problem. If the number or size of components to be mounted on the circuit board 801 is increased, or if incorporate two or more circuit boards, the connector 802 is unable to support the circuit board 801. For example, solder may crack because of excessive load may be applied to a solder joint. Therefore, in order to allow for an increase in the number or sizes of components, or mounting of two or more circuit boards, it is necessary to directly install the circuit board in the enclosure. When the circuit board is directly installed in the enclosure, the position of the circuit board with respect to the enclosure deviates from a reference position in design, within installation tolerance. Further, the position of the connector with respect to the circuit board is also displaced within installation tolerance. The displacements of these positions finally appear as a displacement of the position of the connector with respect to the enclosure. In particular, when a displacement of the position of the circuit board with respect to the enclosure and a displacement of the position of the connector with respect to the circuit board take place in the same direction, the displacements amass, resulting in a larger displacement.
However, the known electronic device 800, shown in FIG. 12, hardly allows for positional displacement between the connector 802 and the enclosure 803. This is because if displacement of the position is increased, there is a possibility that the connector 802 cannot be installed in the enclosure 803. Also, even if the through-hole portion of the enclosure 803 is made larger, there is a possibility that the gap between the enclosure 803 and the connector 802 cannot be filled with the adhesive resin 804.
FIG. 13 illustrates another example of the internal structure of a known conventional electronic device 900, which includes a circuit board 901 fixed to a enclosure 903 having a enclosure main body 903a and a enclosure faceplate 903b, while an internal connector 907 is fixed to the circuit board 901. An external connector 902 is further included, which connects to a mating connector (not illustrated). The external connector 902 has a flange 902a that abuts on a through-hole portion of the enclosure 903. A gap between an abutting surface of the flange 902a of the external connector 902 and the enclosure 903 is sealed by an elastomeric seal 904. The external connector 902 is connected to a relay connector 906 through internal wires 905. The relay connector 906 then connected to the internal connector 907 fixed to the circuit board 901. In the electronic device 900, because the gap between the flange 902a of the external connector 902 and the enclosure 903 is sealed by the seal 904, it is possible to make the through-hole portion of the enclosure 903 larger and also to set a less strict tolerance for the installation position of the external connector 902, as compared to that in the structure shown in FIG. 12. Further, according to the electronic device 900, the position of the external connector 902 with respect to the enclosure 903 is not affected by a displacement in installation position between the circuit board 901 and the enclosure 903 and a displacement in installation position between the internal connector 907 and the circuit board 901.
The electronic device 900, shown in FIG. 13, can improve the degree of flexibility in layout due to the structure using internal wires. On the other hand, however, the electronic device 900 requires the internal connector 907, the relay connector 906 and the internal wires 905 besides the external connector 902, thereby increasing the number of components. Also, connection work and the like within the enclosure 903 are necessary.